Five murine hepatocellular tumor cell lines (HepM-1-5) were isolated and grown in a synthetic medium added with hormones, growth factors and/or serum. The morphology of these lines ranged from a nearly homogeneous epithelial-like shape (HepM-2) to a stromal appearance (HepM-1). The remaining lines displayed a mixed morphology. For their proliferation all of the cell lines retained a clear dependence on the extracellular calcium level and hormonal and/or serum growth factors and, rather homogeneously, they did not express the albumin, alpha-fetoprotein (with the exception of HepM-2 cells), tyrosine aminotransferase, and ornithine transcarbamylase genes, whereas they all exhibited discrete levels of the ornithine aminotransferase mRNA. Only HepM-3 and HepM-5 lines expressed the procollagen type I gene.